I am trying to do a kubectl exec and store value into a variable. But the variable displays null. If i use -it in the exec, it works. Since while running with terraform says can't allocate terminal, I need to run it without -it.
Command I run: abc=$(kubectl exec nginx-6799fc88d8-xpzs9 -- nginx -v)
You need to modify your command as following(-it):
abc=$(kubectl exec -it nginx-6799fc88d8-xpzs9 -- nginx -v)
The reason for this behavior is nginx -v is displaying the output over stderr not stdout. This means, the command you were using would work for any other commands like ls , cat etc which display output over stdout.
Alternate approach by redirecting stderr to stdout(2>&1) :
abc=$(kubectl exec nginx-6799fc88d8-xpzs9 -- nginx -v 2>&1)
Example:
x=$(k exec nginx -- nginx -v 2>&1)
echo "$x"
nginx version: nginx/1.21.3
As #P.... Mentioned alternative approach for replacing -it is using 2>&1
File descriptor 1 is the standard output (stdout).
File descriptor 2 is the standard error (stderr).
-i Pass stdin to the container(stdin)
-t Stdin is a TTY(tty)
Here is one way to remember this construct: at first, 2>1 may look like a good way to redirect stderr to stdout. However, it will actually be interpreted as "redirect stderr to a file named 1". & indicates that what follows and precedes is a file descriptor and not a filename. So the construct becomes: 2>&1.
Consider >& as a redirect merger operator.
For more details, refer this document on kubectl exec command.
Linux (Gentoo) and Linux (Redhat on AWS free)
I am a member of the pcap group and can run tcpdump as a non-root user.
I am trying to run a script the runs tcpdump in the background and send the output to a text file temp.txt. My script will create a file called temp.txt but /usr/bin/tcpdump -tttt will not write to it.
I can run the script without nohup.
/usr/sbin/tcpdump -c 10 -tttt > `pwd`/temp.txt
Why will the nohup not work? The following is my script:
#!/bin/bash
#tpd-txt.sh
nohup /usr/sbin/tcpdump -c 10 -tttt > `pwd`/temp.txt > /dev/null 2>&1 &
Try
nohup /usr/sbin/tcpdump -c 10 -tttt 2>&1 >./temp.txt &
I am assuming you want to redirect standard error to output so it can be captured in logs.
Below is quick reference guide for output redirection in bash.
1>filename
# Redirect stdout to file "filename."
1>>filename
# Redirect and append stdout to file "filename."
2>filename
# Redirect stderr to file "filename."
2>>filename
# Redirect and append stderr to file "filename."
&>filename
# Redirect both stdout and stderr to file "filename."
2>&1
# Redirects stderr to stdout.
# Error messages get sent to the same place as standard output.
Our shell script contains the header
#!/bin/bash -x
that causes the commands to also be listed. Instead of having to type
$ ./script.sh &> log.txt
I would like to add a command to this script that will log all following output (also) to a log file. How this is possible?
You can place this line at the start of your script:
# redirect stdout/stderr to a file
exec &> log.txt
EDIT: As per comments below:
#!/bin/bash -x
# redirect stdout/stderr to a file and still show them on terminal
exec &> >(tee log.txt; exit)
I'm attempting to write a bash script that uses nohup and passes errors to rsyslog.
I've tried this command with different variations of the log variable (see below) but can't get the output passed to anything but a std txt file. I can't get it to pipe.
nohup imageprocessor.sh > "$LOG" &
Is it possible to pipe nohup output or do I need a different command.
A couple of variations of log that I have tried
LOG="|/usr/bin/logger -t workspaceworker -p LOCAL5.info &2"
or
LOG="|logtosyslog.sh"
or
LOG="logtosyslog.sh"
A way in bash to redirect output to syslog is:
exec > >(logger -t myscript)
stdout is then sent to logger command
exec 2> >(logger -t myscript)
for stderr
Not directly. nohup will detach the child process, so piping the output of the nohup command isn't helpful. This is what you want:
nohup sh -c 'imageprocessor.sh | logger'
Is it possible to redirect all of the output of a Bourne shell script to somewhere, but with shell commands inside the script itself?
Redirecting the output of a single command is easy, but I want something more like this:
#!/bin/sh
if [ ! -t 0 ]; then
# redirect all of my output to a file here
fi
# rest of script...
Meaning: if the script is run non-interactively (for example, cron), save off the output of everything to a file. If run interactively from a shell, let the output go to stdout as usual.
I want to do this for a script normally run by the FreeBSD periodic utility. It's part of the daily run, which I don't normally care to see every day in email, so I don't have it sent. However, if something inside this one particular script fails, that's important to me and I'd like to be able to capture and email the output of this one part of the daily jobs.
Update: Joshua's answer is spot-on, but I also wanted to save and restore stdout and stderr around the entire script, which is done like this:
# save stdout and stderr to file
# descriptors 3 and 4,
# then redirect them to "foo"
exec 3>&1 4>&2 >foo 2>&1
# ...
# restore stdout and stderr
exec 1>&3 2>&4
Addressing the question as updated.
#...part of script without redirection...
{
#...part of script with redirection...
} > file1 2>file2 # ...and others as appropriate...
#...residue of script without redirection...
The braces '{ ... }' provide a unit of I/O redirection. The braces must appear where a command could appear - simplistically, at the start of a line or after a semi-colon. (Yes, that can be made more precise; if you want to quibble, let me know.)
You are right that you can preserve the original stdout and stderr with the redirections you showed, but it is usually simpler for the people who have to maintain the script later to understand what's going on if you scope the redirected code as shown above.
The relevant sections of the Bash manual are Grouping Commands and I/O Redirection. The relevant sections of the POSIX shell specification are Compound Commands and I/O Redirection. Bash has some extra notations, but is otherwise similar to the POSIX shell specification.
Typically we would place one of these at or near the top of the script. Scripts that parse their command lines would do the redirection after parsing.
Send stdout to a file
exec > file
with stderr
exec > file
exec 2>&1
append both stdout and stderr to file
exec >> file
exec 2>&1
As Jonathan Leffler mentioned in his comment:
exec has two separate jobs. The first one is to replace the currently executing shell (script) with a new program. The other is changing the I/O redirections in the current shell. This is distinguished by having no argument to exec.
You can make the whole script a function like this:
main_function() {
do_things_here
}
then at the end of the script have this:
if [ -z $TERM ]; then
# if not run via terminal, log everything into a log file
main_function 2>&1 >> /var/log/my_uber_script.log
else
# run via terminal, only output to screen
main_function
fi
Alternatively, you may log everything into logfile each run and still output it to stdout by simply doing:
# log everything, but also output to stdout
main_function 2>&1 | tee -a /var/log/my_uber_script.log
For saving the original stdout and stderr you can use:
exec [fd number]<&1
exec [fd number]<&2
For example, the following code will print "walla1" and "walla2" to the log file (a.txt), "walla3" to stdout, "walla4" to stderr.
#!/bin/bash
exec 5<&1
exec 6<&2
exec 1> ~/a.txt 2>&1
echo "walla1"
echo "walla2" >&2
echo "walla3" >&5
echo "walla4" >&6
[ -t <&0 ] || exec >> test.log
I finally figured out how to do it. I wanted to not just save the output to a file but also, find out if the bash script ran successfully or not!
I've wrapped the bash commands inside a function and then called the function main_function with a tee output to a file. Afterwards, I've captured the output using if [ $? -eq 0 ].
#! /bin/sh -
main_function() {
python command.py
}
main_function > >(tee -a "/var/www/logs/output.txt") 2>&1
if [ $? -eq 0 ]
then
echo 'Success!'
else
echo 'Failure!'
fi